1. Field of the Invention
The invention relates generally to the field of blistering to form thin-films. The thickness of the film is determined by the penetration depth of the implanted ions which is nominally less than several microns. More particularly, the invention relates to an efficient method for transfer of thin-films of SiC utilizing lattice oriented implantation and wafer bonding.
2. Discussion of the Related Art
Thin films of silicon carbide can be cleaved or delaminated from a bulk crystal and transferred to another substrate utilizing implantation and wafer bonding. This process involves implantation of hydrogen into a bulk crystal to produce an implanted layer having a highly damaged (and strained) region near the mean range of the ions. This region can be denoted Rp. The bulk crystal (or the source substrate) is then bonded to another substrate, hereafter referred to as the target, and the bonded pair are then thermally cycled causing the implanted layer to delaminate at or near Rp. This delamination leaves the thin-film bonded to the target substrate as a continuous layer. This process is described in U.S. Pat. No. 5,374,564, the entire contents of which are incorporated by reference, and is known as xe2x80x9cSmart-Cutxe2x80x9d. The implantation of hydrogen is done at room or ambient temperature along a random direction in the bulk single crystal to specifically suppress channeling of the ions in the channels or open spaces of the crystal lattice.
While the process described above has been successfully applied to silicon technology to produce high quality, silicon-on-insulator wafers, it has not been proven successful for the transfer of thin films of SiC of sufficient quality for device applications. A significant problem has been associated with the implantation step. Specifically, light ion implantation of bulk SiC has been shown to deactivate the electrical carriers in the SiC material, making it highly resistive over a depth consistent with the range of the implant. The high resistivity of the implanted SiC material persists even after high temperature annealing at approximately 1300 deg. C. Consequently, the transferred SiC layers have similarly been found to be highly resistive and, therefore, unusable for electronic device applications. Clearly, residual damage produced during hydrogen implantation deactivates or passivertes the carriers. What is needed, therefore, is a solution that permits thin-films of SiC to be transferred, while maintaining the electrical properties as possession in the bulk SiC.
Another problem that has been associated with the implantation step has been excessive roughness of the original and newly exposed (delaminated) thin film surface. What is also needed, therefore, is a solution that permits transfer of a thin film from SiC without the formation of an excessively rough surfaces on either side of the transferred film.
A primary goal of the invention is to provide the use of channeled light-ion (such as, for example, hydrogen or helium) implantation to form a highly strained layer within a single crystal. Another primary goal of the invention is to provide the implantation of light-ions along a random direction in a single-crystal at elevated temperatures.
In accordance with these goals, there is a particular need for channeled light-ion implantation and/or light-ion implantation along a random direction at elevated temperatures to form a highly strained layer within a crystal. Thus, it is rendered possible to satisfy the above-discussed requirement without degrading the electrical properties (e.g. deactivation of the electrical carriers) in the material, which, in the case of the prior art, cannot be satisfied.
A first aspect of the invention is implemented in an embodiment that is based on a method for transfer of a thin-film, comprising: implanting a source crystal with ions along a crystallographic channel of the source crystal to i) form a strained region and ii) define the thin-film; then bonding a surface of the thin-film to a target wafer; and then separating a) the target wafer and the thin-film from b) a remainder of the source crystal along the strained region. A second aspect of the invention is implemented in an embodiment that is based on a method for transfer of a thin-film, comprising: implanting a crystal with ions at an elevated temperature of at least approximately 200xc2x0 C. to i) form a strained region and ii) define the thin-film; then bonding a surface of the thin-film to a target wafer; and then separating a) the target wafer and the thin-film from b) a remainder of the source crystal along the strained region. A third aspect of the invention is implemented in an embodiment that is based on combining the first aspect and the second aspect. A fourth aspect of the invention is implemented in an embodiment that is based on a thin-film comprising: a portion of a target wafer separated from a remainder of the target wafer at a strained region, wherein the target wafer possesses a set of electrical properties and the thin-film substantially maintains the set of electrical properties.
These, and other, goals and aspects of the invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the invention and numerous specific details thereof, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the invention without departing from the spirit thereof, and the invention includes all such modifications.